Within the last several years, public interest in the recycling of plastics has grown significantly. The primary reason for the increased public awareness is the non-biodegradable nature of many plastics; i.e., the chemical stability of plastics that makes their use in products attractive also prevents their decomposition in landfills after use. As such, the public is demanding that these plastic products be recycled into new products rather than being transported to and dumped in a landfill.
A primary difficulty in recycling plastics is that, for a collection of recovered plastic items to be recyclable and therefore valuable, the plastic items must be sorted into smaller collections wherein all items of the fraction are made of the same generic material; only then can they be reground into a form useful in making new products. Generally, the resident or business that discards plastic items probably lacks the expertise to sort the items by material type, nor can the waste collector be expected to be sufficiently knowledgeable to do so. As a result, this sorting is typically performed by hand by those with sufficient experience to recognize different plastics, but this process is extremely labor-intensive and for that reason undesirable, impractical, or even impossible for large amounts of waste plastic.
Plastic bottles are a prolific source of plastic waste, and thus are a primary target for recycling. Plastic bottles are used as containers for such products as carbonated beverages, the bottles for which generally are made of polyethylene terephthalate (PET), milk and household cleaning products, which are bottled predominantly in high density polyethylene (HDPE), and other household goods, which are bottled with polyvinyl chloride (PVC), polypropylene (PP), polycarbonate (PC) and polystyrene (PS). PET bottles often include a colored HDPE basecup, which also must be separated somehow. Bottles of all of these plastic materials generally are collected from the end users as a group, either by a household or by a waste collector, and delivered to a reprocessor in bales. The bales will often contain not only single bottles, but interlocked clusters of bottles that become intertwined as they are crushed during the baling process. To effectively separate all of the bottles in such a group so that the fractions resulting from separation are useful in recycling, and based on current uses of plastics, the mixture should preferably be separated into five fractions: clear PET, green PET, clear HDPE, colored HDPE, and other plastics. It is of particular interest to remove all PVC bottles from PET bottles, as these materials cannot be separated by density, and because a small percentage of PVC in a sample of ground PET will contaminate that sample. The prior art fails to disclose a method of accurately sorting a collection of bottles automatically, or an apparatus designed to perform the sortation.
Accordingly, a first object of the present invention is to provide a method for separating a mixture of individual plastic items wherein each individual item of the mixture is predominately made of a single plastic material, but different individual items are made of different plastic materials, into fractions, each of which contains a single material.
A second object of the present invention is to provide an apparatus for performing the separation.
It is a more particular object to provide a method for separating a mixture of individual plastic bottles into fractions of individual bottles made of the same plastic material. A further object is to provide an apparatus for carrying out the separation method.
The existence of such a separation method in turn raises the need for a method and apparatus to produce a stream of single bottles suitable for separation from the typical bale of crushed bottles. Accordingly, it is a further object of this invention to provide such a method and apparatus.